So far, so good. For any time-strapped fitness enthusiast, the claim is appealing: get ripped and fitter in as little time as possible. And with nearly 900 franchises worldwide across seven countries, including the UK, Australia and Japan, its fan base is undeniable. Determined to sift through the hype, I headed to New York’s Orangetheory Fitness studio to find out.

After logging my weight and height, I was handed a heart-rate strap and ushered into the workout room. There I was met with 15 treadmills, eight rowing machines and a workout area with free-weights, TRX (Total Body Resistance Exercise) straps and the odd weight machine, all illuminated by an orange light.

My instructor, Justin, explained that Orangetheory assumes five different workout “zones” based on your heart rate, from a warm-up zone to the all-out “orange zone”, or your max heart rate. This was where we reach the promised land of afterburn.

A screen with my name, heart rate and minutes in the “orange zone” (known as “splat points”) was viewable throughout the class, along with my class mates’. My competitive spirit was stoked as I compared myself to others, and collectively we were encouraged to get a bigger number of “splat” points as a team.

The next hour was engaging, hard work and fun, and it was over quickly. As a group we were led through an interval workout on the treadmills, following by a circuit of free weights, the rowers or the treadmills. The final section involved a competition where pairs raced in intervals on the rower and the treadmill. I found I was still able to push myself based on my individual heart-rate zone.

At the end of the class, the screen read 508 calories burned, while my personal Garmin heart-rate monitor showed only 412 calories. According to Tom Summers, head strength and conditioning coach at Hong Kong’s Pinnacle Performance, inflation of “calories burned per class” claims are not the only potential downfalls of this type of workout.

“The problem I have with suggesting that you want bigger Epoc is that you ideally don’t want to spend too long getting back to ‘normal’ if you can help it, as it limits how quickly your body is ready to go out and train again.”

He says the 36-hour afterburn claim is also unlikely. “Realistically, the only people who are going to be burning calories for that long after class are those who are so far out of shape that literally climbing a flight of stairs puts them out of breath – and they’re the type of people who really shouldn’t be doing a workout class at 85 per cent of their max heart-rate anyway.”

Research from a team based in South Australia, published in the 2006 Journal of Sports Science, estimated the Epoc increase to metabolism would likely only be six to 15 per cent post exercise, meaning my workout – assuming the Garmin 412 number – burned a maximum extra 62 calories during my Epoc phase.

Summers says the workout after the Epoc stage is not altering your metabolism for the long term. “It doesn’t build muscle mass; it doesn’t change the anatomical condition of your muscles.”

“If you’re truly going to truly ‘burn calories’ and change your body shape, you need to be building muscle mass, as that’s what’s going to fire your metabolism during the days when you’re not exercising,” he says. At Pinnacle Performance, for example, each member is assessed and then set their own programme, specific to their goals – whether it be fat loss, muscle development, or increasing aerobic capacity. Even in group workout classes, members train together but on their own regime.

Marco Ferdinandi, regional fitness operations director of personal training at Pure Fitness, says that Epoc is “really nothing new in the fitness world”.

“Any exercise that increases demand on the all systems in the body – cardiovascular, muscular, nervous, connective tissue – through higher intensity work will lead to increased metabolic activity after the exercise is finished.” He gives High Intensity Interval Training (HIIT) classes, and resistance or circuit training classes performed at a high intensity, as examples.

“Epoc is definitely an added benefit, but it’s not the essential key to weight loss or training programmes,” says Ferdinandi. “It is generally over-hyped and its effects on weight loss are not that great. There is no downside to Epoc itself but the training programmes that lead to greater Epoc are generally higher intensity and should be planned with adequate recovery and regeneration.”

At about HK$280 a class, my hip pocket would be better off if I went for a hard interval jog around the park instead.

Summers is encouraged, however, by the intimate group training setting and the motivational aspects of the class. “Ultimately it appeals to the mass market, and it gets people into the gym. Some people love it, and that’s great – it’s a social thing and a type of entertainment.”

Orangetheory is yet to reach Hong Kong, but Pure Fitness will be launching small-group training classes next year, comprising a 45-minute, multifaceted workout with equipment like “rowers, treadmills, weights, bodyweight workouts and so on”, according to director of group fitness Meech Aspden. If US trends are any guide, Hong Kong will likely see more whole-body interval-training regimes in gyms across the board, incorporating aerobic training and weight training all in one.

Just don’t be under any illusions about the calorie burn advertised – or think that you can sit on the couch later while “working off” your dessert.